1. Field of the Invention
The present invention relates to heat pumps, devices that move heat from a heat source to a warmer heat sink. More specifically, it relates to Bernoulli heat pumps.
2. Discussion of Related Art
Heat engines are devices that move heat from a source to a sink. Heat engines can be divided into two fundamental classes distinguished by the direction in which heat moves. Heat spontaneously flows “downhill”, that is, toward lower temperatures. As with the flow of water, such “downhill” heat flow can be harnessed to produce mechanical work, as illustrated by internal-combustion engines, e.g. Devices that move heat “uphill”, that is, toward higher temperatures, are called heat pumps. Heat pumps necessarily consume power. Refrigerators and air conditioners are examples of heat pumps. Common heat pumps employ a working fluid that transports heat by convection from the source to the sink. The temperature of the working fluid is varied over a range that includes the temperatures of the source and sink, so that heat will flow spontaneously from the source into the working fluid, and from the working fluid into the sink. The temperature variation of the working fluid is commonly effected by compression and expansion of the working fluid.
By contrast, Bernoulli heat pumps create the required temperature variation by converting random molecular motion (reflected in the temperature and pressure of the fluid) into directed motion (reflected in macroscopic fluid flow). A fluid spontaneously converts random molecular motion into directed motion when the cross sectional area of a flow is reduced, as when the flow passes through a nozzle. The variation in temperature and pressure with cross-sectional area is called the Bernoulli principle. Whereas compression consumes power, Bernoulli conversion does not. The energy-conserving character of Bernoulli conversion is the fundamental efficiency exploited by the Bernoulli heat pump.
While the creation of the working-fluid temperature variation exploited by the Bernoulli heat pump consumes no power, its exploitation to pump heat does require the power dictated by the Second Law of Thermodynamics. That is, when equal amounts of heat are added to and removed from the working fluid at different temperatures, the entropy of the working fluid is increased, and an amount of power proportional to the temperature difference must be supplied to restore the entropy. It is this entropy-restoration power that distinguishes the Bernoulli heat pump from a perpetual-motion machine. The ratio of the heat pumped to the work required to restore the entropy is the Carnot efficiency. This power consumption is quantitatively minor, as common heat pumps operate at less than 10% of Carnot efficiency. The more significant power consumption by Bernoulli heat pumps is that due to the entropy increase resulting from viscous dissipation in the boundary layer of the fluid flow. The challenge of Bernoulli heat pump technology is the minimization of these viscous losses.
The Bernoulli effect is well known, best known perhaps, as the basis for aerodynamic lift. Two U.S. patents (U.S. Pat. Nos. 3,049,891 and 3,200,607) describe devices designed to exploit Bernoulli conversion for the purpose of pumping heat. Both patents describe devices which use stationary nozzles to effect the required variation of the cross-sectional area of a fluid flow. Additionally, U.S. Pat. No. 3,049,891 is restricted to supersonic flow.
The present invention, also relates to the use of Ekman flow. Ekman flow is well known. It is discussed, for example, in Section 23 of “Fluid Mechanics” by L. D. Landau and E. M. Lifshitz (Pergamon Press, 1959). Ekman flow forms spontaneously near the surface of a spinning disk. The so-called no-slip property of gas-solid interfaces requires that the gas in the immediate vicinity of a spinning disk move with the disk. Unlike the solid comprising the disk, however, the gas spinning with the disk cannot withstand the concomitant centrifugal force. The resulting outward spiraling flow is called Ekman flow.